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From: wij <wyniijj5@gmail.com>
Newsgroups: comp.theory
Subject: Re: How to write a self-referencial TM?
Date: Thu, 15 May 2025 02:01:55 +0800
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In-Reply-To: <1002l44$2k04b$3@dont-email.me>

On Wed, 2025-05-14 at 18:49 +0100, Richard Heathfield wrote:
> On 14/05/2025 18:33, wij wrote:
> > On Wed, 2025-05-14 at 18:14 +0100, Richard Heathfield wrote:
> > > On 14/05/2025 17:43, wij wrote:
> > > > On Wed, 2025-05-14 at 09:51 -0500, olcott wrote:
>=20
> <snip>
>=20
> > > >=20
> > > > > To make a TM that references itself the closest
> > > > > thing is a UTM that simulates its own TM source-code.
> > > >=20
> > > > How does a UTM simulate its own TM source-code?
> > >=20
> > > It doesn't have to simulate anything. All it has to do is to
> > > restore the state into which the programmer wishes to recurse.
> >=20
> > So, when you say "A UTM simulates X", it means=C2=A0'the UTM' doesn't h=
ave to do
> > anything. So, 'UTM' is human (e.g. you), not a real TM?
>=20
> No, it doesn't mean that.

You said "It doesn't have to simulate anything. All it has to do is to
restore the state into which the programmer wishes to recurse."

Then, what is it?

> >=20
> > > I've already shown how this can be done.
> >=20
> > Where?
> >=20
> Message-ID: <1001bmf$2ao7o$2@dont-email.me>
>=20
> Here's the gist of that article...
>=20
> Here's the tape:
> [0]
>=20
> current state: 0
> content of the square being scanned: 0
> new content of the square: 0
> move left, right, or stay: stay
> next state: 0
>=20
> This TM functions by returning the state of the machine to its=20
> starting state.
>=20
> The only functional difference between this code and yours is=20
> that yours will blow the stack. (Mine doesn't have a stack to blow.)
>=20

1. Apparently your TM (one single symbol '0') is not what you say.
2. D() should have at least one final state